Amylaceous fire-retardant composition



AMYLACEOUS FIRE -RETARDAN T COMPOSITION Grinnell Jones and Walter Jrida,Cambridge, and

Samuel Soil, Boston, Mass., assignors, by mesne assignments, to AlbiManufacturing Co., Incorporated, a corporation of Connecticut NoDrawing. Application August 19, 1942,

Serial No. 455,346

3 Claims. (Cl. 106-15) The present invention relates to a fire-retardantcomposition and more particularly to such a composition suitable forexternal application to wood.

It is an object of the invention to provide an improved fire-retardantcomposition.

The composition of our invention may be ap plied to wood, for example bybrushing or sprayins, either on the finished structure or on the lumberbefore construction, and when so applied, it will substantially reduceboth the danger of ignition and the spreading of fire.

In time of war there is an urgent need for rapid building of fireproofstructures and, at the same time, conventional fire-proof constructionmaterials are diflicult to obtain. By our invention lumber, which isreadily available and admirably adapted to rapid constructionoperations, may be rendered sufiiciently fire-resistant to be anacceptable substitute for conventional fireresistant constructionmaterials.

Our composition contains no chemicals which are injurious to the wood orwhich cause corrosion of nails or other metal adjuncts to the structure.It does not encourage, or even permit, the growth of fungi or bacteriawhich might cause decay. It does not contain any chemicals which areeither poisonous or dangerous to workmen who apply the composition tothe wood or erect structures with treated wood. "The solvent or vehicledoes not give rise to inflammable or explosive fumes.

Our composition, when applied to wooden structures, may, if desired, becovered with a waterproof and weatherproof paint (such as the commonlinseed oil paints) without significantly impairing the fire-retardingqualities of the composition. Many pigments are compatible with thecomposition, whereby any desired color may be imparted to it. Itcontains materials which ar available in large quantities in time of warand which are not in such demand for other war purposes as to bedifllcult to obtain.

Numerous prior proposals have been made for the protection of woodagainst fire, but to the best of our knowledge, none of these proposalshas sufliciently satisfied the numerous and exacting requirements forflreproofing on a commercial scale to be generally adopted and used. Itis well known that certain chemicals, for example ammonium phosphate,borax, and others, have some fire-retarding action. Efforts have beenmade to enhance the eflectiveness of these chemicals by vacuum andpressure tank impregnation into wood, or by'the use of small amounts ofadhesives such as glue, dextrin, or starch to increase the thickness ofthe surface coating on the wood. These proposals have fallen far shortof achieving the desired objectives, as is demonstrated by the limiteduse of these procedures. It has also been proposed to employ thickcoatings of non-combustible mineral matter such as silica, clay, gypsum,or sodium silicate. Such suggestions have not met the requirementsnecessary for commercial acceptance.

In accordance with our invention, fire-resistant and fire-retardantproperties are imparted to wood or other combustible materials byapplying to the same a layer of chemicals which is adherent, stable andpotentiall reactive and which, when subjected to heat, is convertedinto-a layer of carbon which acts as an adsorbent, a heat insulator, anda means of excluding air. At the same time, the carbon layer thus formedis itself rendered substantially non-combustible by the presence thereinof a fire-retarding chemical formed during the heat-induced chemicalreac tion. Thus the wood is protected from damage by destructivedistillation or combustion to a sufficient degree to resist ignition andto prevent the spread of flame.

Our improved composition comprises essentially an activate and anactivator therefor which, at elevated temperatures, will convert theactivate, into a layer of so-called "activated carbon on the surfacewhich has been treated with the composition. I

As the activate, we may use any solid carbonaceous substance which, atelevated temperatures such as the temperature of combustion of wood, orlower, will be converted into carbon. rather than volatilize.Preferably, but not necessarily, the activate should be a substancewhich does not melt at these temperatures and which can be suspended,dispersed or dissolved in aque-- ous media. Carbohydrates generally aresuitable materials for this purpose. Specific mention, by way ofexample, may be made of starch, dextrin, carbohydrate gums, sugar andlike substances. It will be noted that these materials, by themselves,are combustible.

Since the viscosity of the final fluid composition is often an importantconsideration, the activate should be chosen so as to yield a viscositysuit able for the purpose in mind. The viscosity desired for variousmethods of applying the composition may vary considerably. Thus thick orthin boiling varieties of starch, or mixtures thereof, may be used.

As an activatorwe may use chemicals which,

t elevated temperatures such as those indicated bove, will convert theactivate into a carbon iyer, that is, chemicals which. under theinflunce of heat, are capable of forming so-called activated" carbonfrom the activate. Speciiic xamples of chemicals meeting these require-4 grade) in 225 cc. of water. 210 grams of powdered copper sulfate(CuSO4.5H2O) i added to this ammoniacal solution and the mixture isstirred until the copper sulfate is entirely dissolved,

rents include monoammonium phosphate, di-

mmonium phosphate, phosphoric acid, sodium hosphates, zinc chloride,calcium chloride, tin hloride' and other tin salts, aluminum sulfate,Jdium tungstate, boric acid and borates, amionium sulfamate, ammoniumsulfate, and the ke.

Since the activate has a natural tendency to :rment and since someactivators (particularly hosphates) favor this fermentation and therowth of wood-destroying fungi, we find it genrally desirable to includein our composition a mgicide and/or bactericide which will prevent :1egrowth of fungi and bacteria in the treated pod and in the compositionitself. Suitable sub- ;ances for this purpose include copper ammonia11125 (the complex copper ammonia salts are preerred to simple coppersalts since they donot recipitate with many anions such as the phoshateor tungstate ions), borax (if the alkalinity f the latter does notinterfere with the actiator), zinc ammonia salts, fluorides, arsenates,rsenites, organic fungicides and the like.

A binder may also be used, if desired, for enancing the adhesion of ourcomposition to the reated surface and also for increasing the mount ofthe composition adhering thereto; We my use an aqueous emulsion of aresin of the lkyd type, urea formaldehyde resins and others 'hich possesbinding properties. Obviously; the esin must be compatible with theother ingredints so that it will not precipitate from the comosition.The activate itself may be so selected as a impart desirable bindingproperties to the comosition. For example, certain thin boiling vaietiesof starch of high fluidity can be used as oth activate and binder whenthey are boiled 'ith water prior to the addition of the activator.

An ingredient which will improve the waterresting quality of the driedcomposition on the pod, such as a wax, resin, gum, or the like, may eadded if desired.

Pigments or other coloring materials may also eadded.

The composition is dissolved or suspended in a quid medium, preferablywater.

The activate should be present in our compo- .tion in amount betweenapproximately 20% and of the weight of the activator present. We avefound that proportions outside these limits 0 not form an effectiveactivated" carbon layer.

The final liquid composition should contain at :ast 25% by weight of thecombined activate and ctivator. A preferred composition contains 50% yweight of these ingredients.

As one example of a suitable composition falling ithin the scope of ourinvention, the following my be given, it being understood that this is11. istrative only and is not to be construed in a miting sense:

675 grams of a thin boiling starch are stirred ito 2835 cc. of coldwater and the resulting susension is heated to about 80 to 85 C. withcon- ;ant and thorough agitation. The temperature L maintained in theneighborhood of 85 C. for pproximately five minutes and the solution isden cooled, the agitation being continued.

An aqueous ammoniacal solution is made by issolving 225 cc. of ammonia(29.4% technical thereby forming a complex copper ammonia sulfate. Theammonia functions to form a soluble complex copper ammonia salt, thuspreventing subsequent formation of an insoluble copper phosphate whichwould precipitate from the solution. If the fungicide is one which doesnot form an insoluble compound with the activator, it will not bnecessary to add ammonia to the composition.

The ammoniacal copper sulfate solution is added to the starch solutionwhen the latter has been cooled to about 40 C. The copper sulfatesolution should not be added to the hot starch solution because this islikely to result in loss of ammonia and decomposition of the complex copper salt. During the mixing of these two solu-- tions, stirring shouldbe continued for about flve minutes.

To the resulting solution, add 2465 grams of diammonium phosphate inportions of about 300 to 400 grams each with stirring. The smoothness ofthe finalcoated surface may be enhanced byj uslng finely-divideddiammonium phosphate-'for'example mesh. When about half of the phosphatehas been added, the composition thickens noticeably, but after the totalamount has been added, the final composition will again become somewhatmore fluid.

The density of the liquid composition prepared asin the foregoingexample is approximately 1.3. This product is a slurry which, inaddition to the starch and ammonium phosphate which are dissolved in thesolution, contains suspended particles of starch and suspendedundissolved'crystals of ammonium phosphate. Although these suspendedmaterials have a tendency to settle in time, the slurry may readily berestored to a suitable condition for use, by agitation.

, It is not necessary to heat the starch as in the foregoing example. Itmay merely be suspended in cold water by agitation.

In some cases, it may be desirable to add to the composition a resin, asindicatedabove. This resin not only acts as a binder, but will alsoresult in a harder surface, more resistant to abrasion and to moisture,after the composition has been applied to the material to be treated.

Comparative tests have shown that wood treated with our novelcomposition has fire-resistant and fire-retardant properties superior tothose of wood treated only with the same amount of the activator. Theactivate, of course, being combustible, does not of itself impart anyfireresistant properties to the wood. The co-operation of the activatorand activate in producing the fire-resistant properties of ourcomposition is thus clearly demonstrated.

When wood which has been treated with a surface coating of ourcomposition is subjected to the fire tube test developed by the ForestProducts Laboratory of the United States Department of Agriculture[Proc. N. F. P. A. 100-102 (1938) l, a layer of soft, porous carbon isformed on the surface of the wood. At a point a few inches above thecontact of the wood with the flame, this carbon layer, after cooling,feels moist to the touch and the texture of the wood is retained beneaththis layer.

While our invention is, of course, not limited to any particular theoryof operation, it is our belief that this activated carbon layer, formedfrom the reaction of the activator upon the activate in the presence ofheat, functions as a fire-retardant in a number of ways. After theactivated carbon layer has been formed, it may adsorb combustible gasesand vapors such as methane, acetone, etc, which are formed by thedestructive distillation of the wood in direct contact with the flame.It may also adsorb noncombustible gases such as carbon dioxide andnitrogen and thereby interfere with the ignition of the combustiblegases. Moreover, owing to its finely-divided porous condition, the layerof activated carbon may act as an eificient heat insulator and also mayhelp to prevent access of oxygen to the wood. Owing to the presence ofthe activator or of its decomposition products (e. g., phosphoric acidif ammonium phosphate is used as the activator), the activated carbonlayer is itself resistant to combustion.

Our composition may be applied to wood or other combustible material inany convenient manner. While, as previously indicated, it iscontemplated that the composition shall be capable of application bybrushing or spraying, it may also be applied by various knownimpregnation processes if desired. One advantage of our composition,however, is that effective fireretardation may be obtained by surfaceapplication.

Having thus described our invention, we claim:

1. A fire-retardant composition adapted for surface application tocombustible materials, which composition is non-reactive with saidmaterial at ordinary temperatures and comprises an aqueous suspendingmedium having dispersed therein, as the principal ingredients, anactivator selected from the group consisting of ammonium phosphate,ammonium borate, ammonium sulfate, and ammonium sulfamate, and also anamylaceous substance in amount at least but not more than 70% of theweight of said activator, said amylaceous substance being intimatelymixed with but not reacted with said activator, the sum of the weightsOf said activator and said amylaceous substance exceeding of the totalweight of the liquid composition.

20 the liquid composition.

6 2. A fire-retardant composition adapted for surface application tocombustible materials, which composition is non-reactive with saidmaterials at ordinary temperatures and comprises 5 an aqueous suspendingmedium having dispersed therein, as the essential ingredients, ammoniumphosphate and starch, the starch being present in amount of at least 20%but not more than of the weight of the ammonium phosphate,

10 the starch being intimately mixed with but not reacted with'theammonium phosphate, the sum of the weights of the phosphate and starchexceeding 25% of the total weight of the liquid composition.

l5 3. A fire-retardant composition adapted for surface application tocombustible materials as claimed in claim 1 wherein the sum of theweights of the activator and the amylaceous substance is about 50% ofthe total weight of GRINNELL JONES. WALTER JUDA. SAMUEL SOLL.

REFERMCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,329,051 Hunsicker Sept. 7, 1942,106,938 Tramm Feb. 1, 1933 2,033,411 Carson Mar. 10, 1936 2,012,976Schmittutz Sept. 3, 1935 35 1,856,756 Frigiola May 3, 1932 1,501,911Mathias July 22, 1924 276,806 Gfinther May 1, 1883 271,995 Suiiiot etal. Feb. 6, 1883 142,267 Nicoll Aug. 26, 1873 FOREIGN PA'I'ENTS NumberCountry Date 476,043 Great Britain Nov. 29, 1937 435,240 Great BritainSept. 17, 1935 5 334,408 Great Britain Sept. 4, 1930

